Structure for protecting feataures during the removal of sacrificial materials and a method of manufacture therefor

ABSTRACT

The present invention provides a process and an apparatus. The process, in one embodiment, includes providing a micro-electro-mechanical system (MEMS) device, the micro-electro-mechanical system (MEMS) device including an actuator coupled to a movable feature, sacrificial material fixing the actuator and movable feature with respect to one another, and a layer of material located over the actuator, movable feature and sacrificial material. The process may further include removing only a portion of the layer of material to expose the sacrificial material, and subjecting the exposed sacrificial material to an etchant to release the movable feature.

U.S. GOVERNMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Contract No.N66001-04-C-8028 awarded by DARPA under Maskless Lithography.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to microelectronics and,more specifically, to a structure for protecting features during theremoval of sacrificial materials and a method of manufacture therefore.

BACKGROUND OF THE INVENTION

Adaptive optics is a field of optics dedicated to the improvement ofoptical signals using information about signal distortions introduced bythe environment in which the optical signals propagate. An excellentintroductory text on the subject is given in “Principles of AdaptiveOptics” by R. K. Tyson, Academic Press, San Diego, 1991, the teachingsof which are incorporated herein by reference.

Interest in the field of adaptive optics has increased in recent yearsdue to the demand for various adaptive optical elements for use inadvanced applications such as atmospheric imaging, optical signalprocessing, optical data storage, high-power lasers, etc. Arepresentative adaptive optical element is a micro-electro-mechanicalsystem (MEMS) device that may be used, for example, in an optical systemdesigned to compensate for signal distortions introduced in an opticalimage. An appropriate sensor measures the distortions and generatesfeedback for the MEMS device. Based on the feedback, mirrors of the MEMSdevice are deformed such that the distortions are significantly reduced,thus improving receiver performance.

One HEMS device, as might be used in the field of adaptive optics orother related fields, is a deformable mirror. In one instance, adeformable mirror is simulated by an array of very small mirrors, eachhaving a reflective layer, torsional members, support posts, andelectrostatic actuators (e.g., electrodes) positioned thereunder, theelectrostatic actuators configured to control the torsional members, andthus control the shape of the simulated reflective deformable layer. Atypical method for manufacturing such a deformable mirror includesforming the electrostatic actuators, support posts, torsional membersand reflective surface using conventional materials processing, andthereafter releasing the movable elements (e.g., the torsional membersand reflective surface) using a selective etch. Unfortunately, theconventional process for releasing the torsional members and reflectivesurface has various drawbacks, especially when used in conjunction withhybrid devices encompassing the drive circuitry.

Accordingly, what is needed in the art is an apparatus and method ofmanufacture therefore that accommodates the issues related to theaforementioned release step.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides a process and an apparatus. The process, inone embodiment, includes providing a micro-electro-mechanical system(MEMS) device, the MEMS device including an actuator coupled to amovable feature, sacrificial material fixing the actuator and movablefeature with respect to one another, and a layer of material locatedover the actuator, movable feature and sacrificial material. The processmay further include removing only a portion of the layer of material toexpose the sacrificial material, and subjecting the exposed sacrificialmaterial to an etchant to release the movable feature.

As previously discussed, an apparatus is also provided. The apparatus,without limitation, may include an actuator located over a substrate, amovable feature located over and coupled to the actuator, and a layer ofmaterial located above the actuator and movable feature, the layer ofmaterial configured as a reservoir to expose the movable feature.

The foregoing has outlined preferred and alternative features of thepresent invention so that those skilled in the art may better understandthe detailed description of the invention that follows. Additionalfeatures of the invention will be described hereinafter that form thesubject of the claims of the invention. Those skilled in the art shouldappreciate that they can readily use the disclosed conception andspecific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIGS. 1A and 1B illustrate an apparatus configured in accordance withthe principles of the present invention;

FIG. 2 illustrates a SEM image of an alternative apparatus configured inaccordance with the principles of the present invention; and

FIGS. 3 thru 8 illustrate various cross-sectional views illustrating howone skilled in the art might manufacture an apparatus in accordance withthe principles of the present invention.

DETAILED DESCRIPTION

The present invention is based, at least in part, on the acknowledgementthat conventional micro-electro-mechanical system (MEMS) manufacturingsteps, particularly those steps required to release movable feature, areproblematic. More specifically, the present invention has acknowledgedthat the etchant generally used to release the aforementioned movablefeatures may have a negative impact on other components associated withthe MEMS device. For instance, it has been observed that in thosecircumstances wherein the MEMS device is directly coupled to a substrateincluding drive circuitry (e.g., flip-chip bonded to a substrateincluding the drive circuitry) prior to releasing the movable features,the etchant tends to negatively effect, if not destroy, the drivecircuitry when the release occurs.

Based upon the previously discussed acknowledgments and observations,the present invention has recognized that the aforementioned problemsmay be reduced, or even eliminated, by keeping the etchant separate fromany components that it may negatively effect. The present inventionrecognizes that such a separation may be achieved, at least in oneembodiment, by removing only a portion (i.e., less than an entireamount) of a layer of material located over the components to bereleased, a remaining portion of the layer of material helping separatethe etchant from those components that it may negatively effect. Thepresent invention further recognizes, in an alternative embodiment, thatsuch a separation may be achieved by creating a reservoir in the layerof material located over the components to be released, the reservoircontaining the etchtant and thereby helping separate the etchant fromthose components that it may negatively effect.

Turning initially to FIGS. 1A and 1B, illustrated is an apparatus 100configured in accordance with the principles of the present invention.FIG. 1A illustrates a cross-sectional view of the apparatus 100 takenthrough the line A-A of the plan view of FIG. 1B. The apparatus 100 ofFIGS. 1A and 1B includes a MEMS device; however, other embodiments mayexist wherein the apparatus 100 includes various different devices(e.g., other different microelectronic devices) and remain within thepurview of the present invention. Accordingly, the present inventionshould not be limited to any one specific device, and particularlyshould not be limited to the inclusion of a MEMS type device.

The apparatus 100 of FIGS. 1A and 1B initially includes a substrate 110.The substrate 110, in one embodiment, includes drive circuitry or otheractive circuitry configured to operate and/or control the featureslocated thereover. For instance, in the embodiment wherein the apparatus100 includes a MEMS device, the drive circuitry or active circuitrymight be used to effectuate a move therein. Those skilled in the artunderstand the type of circuitry that might be included within thesubstrate 110.

Coupled to the substrate 110 using a bond 115 (e.g., solder bump bond inone embodiment) is a MEMS device 120. The MEMS device 120 illustrated inFIGS. 1A and 1B includes, among other elements, an actuator 130, amovable feature 170 coupled to the actuator 130, and a layer of material180 located above the actuator 130 and movable feature 170. In the givenembodiment of FIGS. 1A and 1B, the MEMS device 120, and moreparticularly a side of the MEMS device 120 opposite the layer ofmaterial 180 is flip-chip bonded to the substrate 110 using the bond115. As is appreciated by those skilled in the art, the drive circuitryin the substrate 110 could thereby provide a drive signal to the MEMSdevice 120 via the bond 115.

The actuator 130 illustrated in the embodiment of FIGS. 1A and 1Bincludes a stationary electrode 140 attached to a support substrate 135.The actuator 130 further includes a movable electrode 145 positionedover the stationary electrode 140. As is illustrated, the movableelectrode 145 may be connected to a spring (flexible beam) 160 by asupport pole 150. Moreover, the spring 160 may be supported over thesupport substrate 135 using one or more anchors 165.

Motion of the movable electrode 145 is transferred to spring 160 viasupport pole 150 and to the movable feature 170 via a support pole 175attached between the spring 160 and the movable feature 170. When avoltage differential is applied between the stationary electrode 140 andmovable electrode 145 of the actuator 130, an attractive electrostaticforce is generated between the electrodes 140, 145 causing the movableelectrode 145 to move toward the stationary electrode 140. Motion of themovable electrode 145 therefore deforms spring 160 (e.g., generating acounteracting spring force), which is transferred to movable feature 170via support poles 150 and 175. When the voltage differential is removed,the spring force of the deformed spring 160 returns the movableelectrode 145 and movable feature 170 to their initial positions.

The movable feature 170 illustrated in FIGS. 1A and 1B comprises amovable reflective feature (e.g., movable mirror). Alternatively,however, the movable feature 170 could comprise a movable membrane, afeature for effectuating movement of a different feature positionedthereover, etc., among other structures. Therefore, the presentinvention should not be limited to any specific movable feature 170.

As was previously indicated, a layer of material 180 is positioned abovethe actuator 130 and the movable feature 170. The layer of material 180may comprise many different materials, configurations and/or placementsand remain within the purview of the present invention. The layer ofmaterial 180 illustrated in FIGS. 1A and 1B comprises silicon, forexample a silicon handle (e.g., original silicon layer) that the movablefeature 170 and actuator 130 were originally formed thereon. In thisembodiment, the layer of material comprising silicon would have athickness (t) ranging from about 100 microns to about 750 microns. Ifthe layer of material 180 were not a silicon handle, the thickness ofthe layer of material 180 might be less than the thickness (t) rangegiven.

The layer of material 180 in the embodiment of FIGS. 1A and 1B isconfigured as a reservoir. As will be understood more fully below, thereservoir configuration of the layer of material 180 is particularlybeneficial to the process for releasing the movable feature 170.Particularly, the reservoir configuration of the layer of material 180substantially, if not completely, confines the etchant used to removethe sacrificial material (e.g., the material that initially fixes themovable feature 170 to the actuator 130). Said another way, thereservoir configuration of the layer of material 180 keeps the etchantaway from unwanted components, for example the drive circuitry of thesubstrate 110.

The apparatus 100 of FIGS. 1A and 1B includes many benefits of otherconventional apparatuses. Foremost, however, the apparatus 100 of FIGS.1A and 1B does not experience the issues generally associated with therelease process, and thus does not experience the reliability issuesexperiences by other conventional apparatuses. Other benefits arenonetheless also achieved.

Turning now to FIG. 2, illustrated is a SEM image of an alternativeapparatus 200 configured in accordance with the principles of thepresent invention. The apparatus 200 of FIG. 2 differs from theapparatus 100 of FIG. 1 in that the apparatus 200 of FIG. 2 includes anarray of actuators and movable features 210 disposed over the substrate.Additionally, a layer of material 220 located above the array ofactuators and movable features 210 is configured as a reservoir toexpose the array of actuators and movable features 210, while confiningthe aforementioned etchant. The apparatus 200 of FIG. 2 illustrates thatthe layer of material 220, and more particularly the reservoir in thelayer of material 220, need not be confined to a device-by-device basis(e.g., a single MEMS feature), but can be easily configured for an arrayof devices.

Turning now to FIGS. 3 thru 8, illustrated are various cross-sectionalviews illustrating how one skilled in the art might manufacture anapparatus in accordance with the principles of the present invention.The apparatus 300 illustrated in FIG. 3 initially includes components ofa MEMS device 305, including a layer of material 310, a movable feature315, and an actuator 320, among others. The layer of material 310, inone particular embodiment, comprises silicon, such as what might befound in a silicon wafer or silicon handle. In those embodiments whereinthe layer of material 310 comprises silicon from a silicon wafer orsilicon handle, the layer of material 310 might have a thickness (t)ranging from about 100 microns to about 750 microns, among others. Inalternative embodiments, the layer of material 310 comprises a materialdifferent than silicon, for instance silicon carbide or another similarmaterial. In those embodiments, the thickness (t) of the layer ofmaterial 310 might differ from the range set forth above.

In the embodiment of FIG. 3, an etch stop layer 312 is formed over thelayer of material 310. The etch stop layer 312 in one embodiment is anoxide portion of a silicon-on-insulator (SOI) structure. The etch stoplayer 312, in alternative embodiments, might comprise a differentmaterial. The etch stop layer 312 may include many differentthicknesses.

Formed over the layer of material 310 and etch stop layer 312 is themovable feature 315 and actuator 320. As is illustrated, the movablefeature 315 is coupled to the actuator 320 using a support pole 318. Themovable feature 315, without limitation, may comprise a materialcommonly used in the manufacture of microelectronic devices, forinstance polysilicon, silicon, etc.

The actuator 320 illustrated in the embodiment of FIG. 3 includes aspring (flexible beam) 330 connected to the movable feature 315 usingthe aformentioned support pole 318. Coupled to the spring 330 using asupport pole 335 is a movable electrode 340. The actuator 320 furtherincludes a stationary electrode 350 attached to a support substrate 360,and disposed a distance from the movable electrode 340. As isillustrated, multiple anchors 345 may support and separate the spring330 (and thus the movable electrode 340) and the support substrate 360(and thus the stationary electrode 350). The components of the actuator320, again without limitation, may comprise a material commonly used inthe manufacture of microelectronic devices, for instance polysilicon,etc.

In the illustrative embodiment of FIG. 3, the movable feature 315 andthe actuator 320 are fixed with respect to one another. For instance, atthis stage of manufacture, a sacrificial material 370 is used to fix thefeatures 315, 320, with respect to one another. The sacrificial material370, in one embodiment, comprises a silicon oxide (e.g., silicondioxide). The skilled artisan understands that the sacrificial material370 could comprise other materials.

The MEMS device 305 illustrated in FIG. 3 may, in one embodiment, beformed using conventional manufacturing processes. For instance, knowingthe unique layout and order of formation of the features of the MEMSdevice 305, one skilled in the art would understand what manufacturingprocesses might be required to follow that layout and order offormation, and thus result with an apparatus 300 similar to that of FIG.3. Accordingly, while the layout and order of forming the features ofthe MEMS device 305 is not well-known (i.e., is unique), themanufacturing process used to achieve the layout and order of formingthe features may be conventional. Because the manufacturing processrequired to achieve the apparatus 300 of FIG. 3 is conventional, nofurther detail is needed.

Turning now to FIG. 4, illustrated is the apparatus 300 of FIG. 3 afterinverting the MEMS device 305 and flip-chip bonding it to a substrate410. The substrate 410, in one embodiment, includes drive circuitry orother active circuitry configured to operate and/or control the featureslocated thereover. For instance, in the embodiment wherein the apparatus300 includes the MEMS device 305, the drive circuitry or activecircuitry might be used to effectuate a move therein. Those skilled inthe art understand the type of circuitry that might be included withinthe substrate 110, thus no further detail is given.

In the illustrative embodiment shown, the MEMS device 305 is flip-chipbonded to the substrate 410 using a bond 420. The bond 420 may comprisemany different bonds; however, one embodiment uses a solder bump bond tophysically and electrically coupled the MEMS device 305 and thesubstrate 410. The process that might be used to bond the MEMS device305 to the substrate 410 may be conventional, including placing the MEMSdevice 305 in contact with the substrate 410 with solder therebetween,and heating the MEMS device 305, substrate 410 and solder past a reflowtemperature of the solder, thereby forming the bond 420.

Turning now to FIG. 5A, illustrated is the apparatus 300 of FIG. 4 afterremoving only a portion (i.e., less than an entire amount) of the layerof material 310, thereby exposing the sacrificial material 370. In theembodiment shown in FIG. 5A, a remaining portion of the layer ofmaterial 310 forms a reservoir 505 (e.g., dam). The remaining portion ofthe layer of material 310, however, may comprise other configurations orshapes and remain within the purview of the present invention.

The process for removing only a portion of the layer of material 310 mayvary greatly based upon the size of the opening, type of material thatthe layer of material 310 comprises, as well as other factors. In oneembodiment, however, a fixture could be used to expose the area of thelayer of material 310 that should be removed, such that an etchant(e.g., a selective etchant) could be used to remove the desired portionof the layer of material 310. As those skilled in the art appreciate,the etch stop layer 312 is configured to substantially prevent theetchant from etching into the movable feature 315. Accordingly, the etchstop layer 312 would be removed after forming the reservoir 505 in thelayer of material 310.

Turning briefly to FIG. 5B, illustrated is a cross-sectional view of anembodiment of a fixture 500 that might be used to remove the portion ofthe layer of material 310 from the apparatus 300. The fixture 500, inthe embodiment shown, includes a first pressure plate 510 and a secondpressure plate 520, wherein a spring 530 is connected to the secondpressure plate 520 to maintain the apparatus 300 in the correctposition. The fixture 500 of FIG. 5B further includes a spacer 540placed between the first and second pressure plates 510, 520, the spacer540 typically being roughly the same thickness as the apparatus 300. Thefixture 500 additionally includes a gasket 550, such as a viton gasket,which specifically defines the area for removal of the layer of material310 (FIG. 5A). The gasket 550 additionally seals the other areas of thelayer of material 310 (especially the other areas of the apparatus 300,including the substrate 310) from the etchant used to remove the portionof the layer of material 310.

The fixture 500 might be used by placing the apparatus 300 between thefirst and second pressure plates 510, 520, such as is shown in FIG. 5B.In doing so, an opening 560 exposes the appropriate area of the layer ofmaterial 310 in the apparatus 300. Thereafter, the apparatus 300, andmore specifically the layer of material 310, could be subjected to aselective removal process (e.g., a wet or dry etch) through the opening560. After removing any remaining etch stop layer 213, what might resultis an apparatus similar to the apparatus 300 illustrated in FIG. 5A.While the fixture 500, and a process for using the fixture 500 has beendescribed within this and the preceding paragraph, those skilled in theart appreciate that other fixtures and processes might be used to removeonly the portion of the layer of material 310.

Turning now to FIG. 6, illustrated is the apparatus 300 of FIG. 5A asthe exposed sacrificial material 370 is being subjected to an etchant610 to release the movable feature 315. More specifically, in theembodiment of FIG. 6 the etchant 610 is being placed within thereservoir 505 formed within the layer of material 310 to release themovable feature 315. Advantageous to the present invention, theremaining portion of the layer of material 310 protects various otherfeatures of the apparatus 300 from the etchant 610. Accordingly, anydrive circuitry or other sensitive circuitry in the substrate 410 issubstantially protected from the etchant 610.

In the embodiment wherein the sacrificial material 370 comprises silicondioxide, the etchant 610 might be hydrofluoric acid or another similarselective etchant. In this embodiment, it is desirable that thehydrofluoric acid should be dispensed in an amount sufficient to removethe entire sacrificial material 370, but an amount not too large as toescape the bounds of the remaining portion of the layer of material 310.In other embodiments wherein the sacrificial material comprises adifferent material, a different etchant 610 might be used.

At this stage in the manufacture of the apparatus 300, that is aftersubjecting the sacrificial material 370 to the etchant 610, theapparatus 300 might be subjected to a diluting bath (e.g., a methanolbath) to neutralize the effects of the etchant 610. Thereafter, theapparatus 300 might be inserted into a critical point dryer, amongothers, to substantially dry the resulting apparatus 300. Given all theprevious discussions, those skilled in the art would understand thisprocess of neutralizing and drying the apparatus. Accordingly, nofurther detail is given.

Turning now to FIG. 7, illustrated is the apparatus of FIG. 6 afterreleasing the movable feature 315 by removing the sacrificial material370. The resulting apparatus 300, as one skilled would expect, wouldgenerally still have the remaining portions of the layer of material310. In many, if not most instances, the remaining portions of the layerof material 310 would remain.

Turning lastly to FIG. 8, illustrated is the apparatus 300 of FIG. 7after forming a layer of reflective material 810 over the movablefeature 315. The reflective material 810, if used, could comprise manydifferent materials and remain within the purview of the presentinvention. Additionally, conventional processes might be used to formthe layer of reflective material 810, again only if this layer was used.

The process of FIGS. 3 thru 8 illustrates but one embodiment. Forexample, another embodiment might exist wherein multiple apparatusessimilar to the apparatus 300 of FIGS. 3 thru 8 are formed on a singlelayer of material 310. In that embodiment, multiple reservoirs 505 wouldbe formed within the layer of material 310 to expose each of themultiple apparatuses. In such an embodiment, the etchant 610 couldsimultaneously be used to release multiple movable features 315.Accordingly, the multiple apparatuses would be formed in parallel. In anadditional embodiment, each of the multiple apparatuses could then belaterally separated from one another, for example by dicing. What wouldresult would be multiple, but separate, apparatuses that were formedusing the same processing steps.

The process described with respect to FIGS. 3 thru 8 also provides manybenefits over prior art processes. The main benefit, however, is theability to use the layer of material, which is preexisting in certainembodiments, to shield sensitive circuitry from the etchant used torelease the movable features of the apparatus.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. A process, comprising: providing a micro-electro-mechanical system(MEMS) device, the micro-electro-mechanical system (MEMS) deviceincluding an actuator coupled to a movable feature, sacrificial materialfixing the actuator and movable feature with respect to one another, anda layer of material located over the actuator, movable feature andsacrificial material; removing only a portion of the layer of materialto expose the sacrificial material; and subjecting the exposedsacrificial material to an etchant to release the movable feature. 2.The process of claim 1 wherein removing only a portion includes forminga reservoir in the layer of material and further wherein subjectingincludes placing the etchant within the reservoir to release the movablefeature.
 3. The process of claim 1 wherein subjecting includingsubjecting the sacrificial material to an etchant including hydrofluoricacid.
 4. The process of claim 3 further including placing themicro-electro-mechanical system (MEMS) device in a diluting bath afterthe subjecting, and then inserting the micro-electro-mechanical system(MEMS) into a critical point dryer.
 5. The process of claim 1 furtherincluding placing a reflective material over the movable feature aftersubjecting.
 6. The process of claim 1 further including flip-chipbonding a side of the micro-electro-mechanical system (MEMS) deviceopposite the layer of material to a substrate including drive circuitry,the flip-chip bonding occurring prior to subjecting.
 7. The process ofclaim 6 wherein a remaining portion of the layer of material protectsthe drive circuitry from the etchant.
 8. The process of claim 1 whereinproviding includes forming the layer of material, forming the movablefeature over the layer of material, and then forming the actuator and atleast a portion of sacrificial material over the layer of material. 9.The process of claim 1 wherein the layer of material has a thicknessranging from about 100 microns to about 750 microns.
 10. The process ofclaim 1 wherein the layer of material comprises silicon.
 11. The processof claim 1 wherein removing includes removing using a process that isselective to the layer of material.
 12. An apparatus, comprising: anactuator located over a substrate; a movable feature located over andcoupled to the actuator; a layer of material located above the actuatorand movable feature, the layer of material configured as a reservoir toexpose the movable feature.
 13. The apparatus as recited in claim 12wherein the actuator and movable feature are a first actuator and firstmovable feature, and further including a plurality of other actuatorsand movable features located over the substrate and configured as anarray of actuators and movable features.
 14. The apparatus as recited inclaim 13 wherein the layer of material is configured as a reservoir toexpose the array of movable features.
 15. The apparatus as recited inclaim 12 wherein the layer of material has a thickness ranging fromabout 100 microns to about 750 micros.
 16. The apparatus as recited inclaim 12 wherein the layer of material comprises silicon.
 17. Theapparatus as recited in claim 12 wherein the movable feature is amovable reflective feature.
 18. The apparatus as recited in claim 12wherein the actuator, movable feature and layer of material form atleast a portion of a micro-electro-mechanical system (MEMS) device. 19.The apparatus as recited in claim 18 wherein the substrate includesdrive circuitry.
 20. The apparatus as recited in claim 19 wherein a sideof the micro-electro-mechanical system (MEMS) device opposite the layerof material is flip-chip bonded to the substrate including the drivecircuitry.